The invention relates to a multi-joint crank drive of an combustion engine with at least one coupling member which is supported on a crankpin of a crank shaft for rotation about a coupling member rotation axis, and at least one connecting rod supported on a crankpin of an eccentric shaft for rotation about an eccentric shat rotation axis, wherein the coupling member is connected with a piston rod of a piston of the combustion engine for pivoting about a piston rod rotation axis and is connected with the connecting rod for rotation about a connecting rod rotation axis, wherein the coupling member has a bearing eye which receives the crankpin of the crankshaft and wherein a coupling angle between an imagined straight line through the coupling member rotation axis and the connecting rod rotation axis on the one hand and an imagined straight line through the coupling member rotation axis and the piston rod rotation axis on the other hand is at least 140 and at most 180. The invention further relates to an internal combustion engine with a multi-joint crank drive.
The multi-joint crank drive of the aforementioned type is for example a component of the combustion engine, but may also be used in other applications. The multi-joint crank drive includes the eccentric shaft whose rotation angle is preferably adjustable by means of an actuator, in particular in dependence on an operating point of the combustion engine. As an alternative or in addition the eccentric shaft can also be operatively connected with the crankshaft of the internal combustion engine and can thus be driven by the internal combustion engine. The multi-joint crank drive has the coupling member, in particular a number of coupling members that corresponds to the number of pistons of the internal combustion engine. The coupling member or the coupling members are respectively rotatably supported on the corresponding crankpin of the crankshaft. Preferably the coupling member has two arms that protrude over the crankshaft on two opposing sides, and which are each provided at their ends with a pivot joint. Of course also other embodiments are conceivable. The rotation axis of the coupling member about the crankshaft or about the crankpin of the crankshaft is referred to as coupling member rotation axis.
One of the pivot joints serves for pivotal connection with the piston rod, which connects one of the pistons of the internal combustion engine with the crankshaft via the coupling member. The rotation axis of this pivot joint is referred to as piston rod rotation axis. Due to the pivotability of the coupling member the piston rod rotation axis is not fixed in position but is displaced or pivoted together with the coupling member. Another one of the pivot joints serves for pivotal connection with the co-called connecting rod, which is supported with its other end, which is opposite the coupling member, on the crankpin of the eccentric shaft. The rotation axis of this pivot joint is referred to as connecting rod rotation axis, while the rotation axis of the connecting rod on the crankpin of the eccentric shaft is hereinafter referred to as eccentric shaft rotation axis.
The connecting rod has for forming the pivot joints preferably two conrod eyes. The first conrod eye is a component of the pivot joint via which the connecting rod interacts with the coupling member. The first conrod eye hereby for example engages around a coupling pin or bearing pin, which is held on the coupling member. The second conrod eye, is analogously a component of the pivot joint via which the connecting rod is connected with the eccentric shaft. In particular the second conrod eye engages around the crankpin of the eccentric shaft at least in regions.
By means of the multi-joint crank drive the compression ratio that is achieved in the cylinder that is respectively assigned to the piston can be adjusted, in particular in dependence on an operating point of the internal combustion engine and/or the actual work cycle. For adjusting the compression ratio the eccentric shaft is caused to assure a defined rotary position that corresponds to the desired compression ratio and/or the phase position between the eccentric shaft and the crankshaft is set to a defined value.
The support of the coupling member on the crankshaft or the crankpin of the crankshaft is realized by means of the bearing eye. The bearing eye hereby is constructed for example in the form of a conrod eye. For example the bearing eye is realized as recess of he coupling member in which the crankpin is arranged and traverses, preferably completely, the bearing eye. The support of eh coupling member on the crankpin of the crankshaft is for example configured as sliding bearing. As an alternative also a rolling bearing possible.
From the state of the art for example the document DE 10 2005 054 761 A1 is known. This document describes an internal combustion engine with a piston which is displaceably arranged in a cylinder in a housing, and which is pivotally coupled with a piston rod whose movement is transferable to a crankpin of a crankshaft. Between the piston rod and the crankpin a transmission member is provided which is constructed as a transverse lever, which is coupled via a joint with the crankpin at a joint point. This joint is situated in a region between a first bearing point of the transverse lever to the piston rod and a second bearing point of the transverse lever to the auxiliary connecting rod and the joint is arranged between the transverse lever and the crankpin at a distance to the connecting line between the two bearing points of the transverse lever to the auxiliary connecting rod and the piston rod.
In a main view of the transverse lever, the transverse lever is superimposed with a plan orthogonal axis system, wherein the zero point of the axis system is arranged in the point of articulation. A first axis extends through the second bearing point. A second axis is perpendicular to the first axis. Both axes divide a drawing plane into four quadrants in a mathematically conventional manner. The first bearing point is arranged in the second quadrant and a center of mass of the transverse lever in the second, the third or the fourth quadrant. The movement of the transverse lever is conducted via the auxiliary connecting rod, which is pivotally supported in the housing on its end, which faces way form the transverse lever.
From the state of the art also the documents JP 2004-124775 A and EP 1 180 588 A2 are known.
Generally the configuration of the internal combustion engine and thus also of the multi-joint crank drive has the goal to reduce the weight, in particular of moving parts as far as possible in order to keep resulting mass forces and the resulting mass-proportional positional forces as low as possible.